The present invention relates to various types of explosion-proof apparatuses installed in a petrochemical plant and the like, and more particularly to an explosion-proof apparatus with a heating means and heating target, and a gas chromatograph for a process.
Generally, in a petrochemical process or steel process, a gas chromatograph for a process has conventionally been used as an apparatus for analyzing the composition of a process gas, monitoring each process step on the basis of the analysis result, and performing various types of control operations.
In a gas chromatograph of this type, a measurement gas (sample gas) to be measured which is sampled from a process line is fed to a column by a carrier gas, and is separated into respective components in the column by utilizing the difference in moving speed based on differences in adsorptivity (affinity) or partition coefficient of the respective components with respect to a stationary phase. The separated gas components are detected by a thermal conductivity detector. The detection values are converted into electrical signals, and waveform-processed by a controller. Based on the waveform-processed signals, the composition of the measurement target gas is analyzed. The process is controlled based on the analytic values, and the chromatogram waveforms are recorded by a recorder.
A gas chromatograph has an analyzer unit with a valve for switching flow paths for the sample gas and carrier gas, a column for separating the sample gas into the respective gas components, a detector for detecting the gas components, and the like, an electrical apparatus portion for driving and controlling the gas chromatograph, and the like. In the analysis of the sample gas, when the temperatures of the column flow path selector valve, sample gas, detector, and the like fluctuate (decrease), the gas components (heavy components) are condensed, and the concentrations of the components do not match the original sample concentrations. Hence, in order to guarantee correct measurement, a heating means for heating the analyzer unit and a thermostatic chamber for keeping the temperature of the analyzer unit are provided.
When a gas chromatograph of this type is installed in a petrochemical plant or the like, if a combustible gas enters the gas chromatograph to come into contact with an electrical circuit portion, it may explode. For this reason, the gas chromatograph must have a predetermined explosion-proof structure in the same manner as various types of electrical meters.
Japanese Patent Laid-Open Nos. 4-248320 and 4-259856 disclose a chromatograph in which a thermostatic chamber is disposed in a pressure resistant explosion-proof case and an analyzer unit and heating means are built into the thermostatic chamber. In this arrangement, the heating means and thermostatic chamber keep the column and flow path control valve to a temperature optimum for separating and analyzing the sample gas.
When the analyzer unit is disposed in the thermostatic chamber in this manner to control the sample gas and carrier gas to a predetermined temperature, the thermal conductivity of the gas can be measured at high precision. Since the heating means to which a voltage that can generate electric spark is disposed in the pressure resistant explosion-proof chamber, even if explosion occurs in the case, the flame is prevented from leaking outside.
In the conventional gas chromatograph, since the thermostatic chamber is built into the pressure resistant explosion-proof case and the analyzer unit and heating means are disposed in the thermostatic chamber, the internal volume of the pressure resistant explosion-proof case increases, and the outer size of the pressure resistant explosion-proof case also increases accordingly. When the internal volume of the pressure resistant explosion-proof case increases, when an explosion occurs, the explosive pressure generated in the pressure resistant explosion-proof case increases, and the flame tends to leak outside. In order to reliably prevent flame leakage to the outside, a long explosion-proof spacing must be formed, and at least the wall thickness defining the explosion-proof spacing must be increased. As a result, in the conventional gas chromatograph, size, weight, and cost reductions are limited.
This problem arises not only in a gas chromatograph for a process, but is common among various types of explosion-proof apparatuses in general each installed in a petrochemical plant or the like and having in it a heating target and a heating means for the heating target.
It is an object of the present invention to provide an explosion-proof apparatus in which the size, weight, and cost of its pressure resistant explosion-proof case can be reduced, and a gas chromatograph for a process.
In order to achieve the above object, according to the present invention, there is provided an explosion-proof apparatus comprising a pressure resistant explosion-proof case, heating means disposed in the pressure resistant explosion-proof case, a heat conduction member heated by the heating means in the pressure resistant explosion-proof case and adapted to supply heat from the heating means to an outside of the pressure resistant explosion-proof case by heat conduction, and a heating target disposed outside the pressure resistant explosion-proof case in contact with the heat conduction member and heated by heat supplied from the heat conduction member.